1. Field of the Invention
This invention relates to a cross shaft member. More specifically, the invention relates to a cross shaft member for forming a cross shaft joint (universal joint) used in a propeller shaft, an intermediate shaft of a vehicular steering apparatus or the like.
2. Related Art
In a vehicular steering apparatus, etc., a cross shaft joint has been used for interconnecting two shafts (not disposed on a common axis) in a torque-transmitting manner. This cross shaft joint comprises a cross shaft member having four shaft portions arranged in a generally cross-shape on an outer periphery of a body portion thereof, a plurality of rows of cylindrical rollers (rolling elements) provided respectively around the shaft portions, and bearing cups (outer rings) mounted respectively around the rows of cylindrical rollers, an outer peripheral surface of each shaft portion being used as an inner ring raceway surface for the cylindrical rollers (see, for example, JP-A-2005-351401).
Like other devices or members used in a vehicle, the above cross shaft joint has also been required to have a lightweight design and a compact design. Therefore, as shown in FIG. 7, a recessed portion 23 is formed in a central portion of a body portion 22 of a cross shaft member 21 forming a cross shaft joint. In this case, the body portion 22 has a brim surrounding the recessed portion 23, and those portions (brim portions) 22a of the brim each disposed between any two adjacent shaft portions 24 is thickened in order to enhance a static strength of the cross shaft member 21.
Although the lightweight design is achieved by forming the recessed portion in the central portion of the body portion, the static strength is inevitably reduced as compared with the case where such recessed portion is not formed, and particularly it has been desired to increase the static strength of the brim portions 22a on which a load concentrates depending on operating conditions, etc.
On the other hand, the static strength can be increased if the recessed portion is not formed in the body portion. In this case, however, the weight of the cross shaft member much increases, and this can not meet the above requirement of the lightweight design.